Moon traverses so small a chord of this shadow, that the whole of her surface is not darkened. In order to distinguish the greatness of Partial Eclipses, it is usual to conceive the Moon's diameter as divided into twelve parts, called Digits; and to say, there are so many digits eclipsed, as there are such parts covered by the Earth's shadow, when the Eclipse is at the greatest.-In all these Eclipses of the Moon", she enters the Western side of the shadow with her Eastern side; and so it is her Western side, which quits the shadow when the Eclipse ceases. 49. Eclipses of the Sun are also distinguished as Total, that is, when the Moon covers the whole body of the Sun from us, and as Partial, when she covers only a part of the Sun. When there is a Total Eclipse of the Sun, it is so dark, that the Stars appear very visible, and there is even need of lamp-light; but, this total darkness, even under the most favourable circumstances, never lasts more than about five minutes; for, as soon as a very small part of the Sun's disc becomes uncovered, it affords us considerable light. But it has been already observed, that, although the Earth can eclipse the whole enlightened hemisphere of the Moon, and so involve the whole of her body in darkness, at the same time; yet, that the Moon (in consequence of her being so much smaller than the Earth) can never obscure more than a small part of the Earth, at the same time. This will be seen, by referring to fig. 13 of Plate II., where the Moon's shadow only covers a small part of the illuminated surface of the Earth (viz. that between C and D), so as totally to hide the Sun's rays from it; whilst, to the inhabitants of the adjoining tracts B C and D E, the Sun will appear to be but partially eclipsed; and, beyond this last (as is evident from the figure) there will be no eclipse of him at all. It happens sometimes, that a Central eclipse of the Sun is not a Total eclipse, but that there is a ring, or circle, of light all round the edge of the Moon (as in fig. 14), wherefore, such an eclipse is said to be annular. This annular appearance is occasioned by the conical shadow of the Moon being too short to reach quite to the Earth, owing to the Moon being in her Apogee: it may be better understood by referring to Plate II. fig. 7, and supposing S to represent the Sun, T the Moon and E the Earth.-In the greatest eclipses of the Sun, the Moon's shadow passes along the middle of the Earth; and such eclipses happen, when the Moon is in a Node at the moment of her Change. If she be not far from a Node, a part of her shadow will fall on some tract of the Earth, and there make a Total, or, at least, a Partial eclipse; and, in proportion as she is nearer to her Node and her Perigee, will be the greatness and length of the obscuration. 50, THE TIDES are caused chiefly by the attraction of the Moon, but partly by that of the Sun. The Sea flows (i. e. rises) as often as the Moon passes the meridian, both the arc above, and the arc below the horizon; and it ebbs (i. e. falls) as often as she passes the horizon, both East and West. When the Moon is in the first, and third quarter (i. e. when she is new and full), the tides are high and swift, and are called springtides; when she is in the second, and last quarter (i. e. when 40 Te quoque, Luna, traho, quamvis Temesæa labores Ovid. Met. VII. 207. In allusion to the superstitious practice of beating brazen vessels, or sounding trumpets during an eclipse of the Moon, when she was thought to be under the power of some spells or incantations. 41 Citharâ crinitus Iopas Personat auratâ, docuit quæ maximus Atlas. Virg. En. I. 742. she is a half-moon), the tides are lower and slower, and are called neap-tides 42. $42. 51. But the lowest, as well as the highest water, will be found at the spring-tides; the neap-tides neither rising so high, nor falling so low: those spring-tides, which happen at the time of the equinoxes, and whilst the Moon is in her Perigee, are always the highest.-The Sea is observed to swell and flow from South to North for about six hours, after which it seems to rest for about a quarter of an hour; it then begins to fall and retire back again from North to South for six hours more, when, after an apparent pause of a quarter of an hour, it begins to flow again as before. Thus the sea flows and ebbs alternately twice a day, but not at the same hours; for the tides return later and later every day by 50 minutes, which is the excess of a lunar day above a solar one. 52. Though the action of the Moon has the greatest share in producing the tides, yet the action of the Sun adds sensibly to it when they unite their forces together, as is the case at the full and change of the Moon, when they are nearly in the same line with the centre of the Earth. Thus, at the change, when they are both on the same side of the Earth, they both conspire to raise the water in the zenith, and, consequently, in the nadir; but, when the Moon is at the full, and the Earth is between her and the Sun, one causes high water in the zenith and nadir, whilst the other does the same in the nadir and zenith: consequently, these are the highest tides, and are what are called Spring-tides. Farther, the action of the Sun diminishes the effect of the Moon's action in the first and last quarters, because the one raises the water whilst the other depresses it; then, therefore, the tides are the least, and are called the Neap-tides. But it must be observed, that the spring-tides do not happen precisely at new, and full moon, nor the neap-tides at the quadratures, but a day or so afterwards; because, as in other cases, so in this, the effect is not greatest or least, when the immediate influence of the cause is greatest or least. This may be also observed with respect to the greatest heat and cold, which are not felt on the Solstitial days, when the action of the Sun is greatest and least. The tides rise to different heights in different parts of the world; in the Bristol Channel they rise above forty feet, and on the Eastern coast of North America more than fifty feet; but their average height is considerably under twenty feet. "These are thy glorious works, Parent of good, Thus wondrous fair: Thyself how wondrous then, In these thy lowest works; yet these declare Him first, him last, him midst, and without end." Milton, Par. Lost, Book V. 153. 42 Qualis ubi alterno procurrens gurgite pontus, Virg. En. XI. 624. CHAPTER II. ORBIS TERRARUM.1 1. GEOGRAPHY is that Science which teaches the knowledge of the Earth; it derives its name from the Greek words. yñ the earth, and ypápw to describe. 2. According to its strict etymology, Geography denotes the description of the Earth only, and is thus distinguished from Hydrography, which refers to the description of the Sea, or Water (ödwp); but, as earth and sea are generally considered by Geographers, as the great component parts of the Terraqueous Globe, hence, the description of them both is generally included in the term Geography. In either of these senses, it differs from Cosmography, which is a description of the Universe (kooμoc), as a part differs from the whole; and also from Chorography, which is the description of a country (xúpa), and from Topography, which is the description of a place (τóñoç), as the whole differs from a part. 3. The situation of places is determined as to North or South, by their latitude, and as to East or West, by their longitude; and these distances are reckoned in degrees and minutes. Every circle, whatever may be its diameter, is divided into 360 degrees; this arose from the ancients supposing that the great circle in the heavens, called the Ecliptic, was traversed by the Sun in 360 days, and hence, they named each day's progress, which he made along this circle, a gradus, step or degree. Each Degree is subdivided into 60 minutes (or miles), and each minute into 60 Seconds, and these are denoted by the signs °,', "; thus 51°. 30'. 45" means 51 degrees, 30 minutes, 45 seconds: moreover, N. stands for North, and S. for South Latitude, E. for East, and W. for West Longitude. 4. The Latitude of a place is its nearest distance from the Equator, either North or South; when the place is North of the Equator, it is said to be in North Latitude, when South of the Equator, it is in South Latitude. And, because the Equator Terra pilæ similis, nullo fulcimine nixa, Ovid. Fast. VI. 271. Orbis, however, is sometimes put for a part of the Earth, and was frequently used by the Romans to denote their extensive Empire. quibus actus uterque Europæ atque Asia fatis concurrerit orbis. Virg. En. VII. 224. divides the Earth into two equal parts, which, again, are divided by the Axis of the Earth into two other equal parts, therefore, the whole great Meridian circle of the Earth is divided into four equal parts: and, as every circle contains 360 degrees, therefore, a fourth part of a circle can contain only 90 degrees. Hence it follows, that Latitude, which is the distance of a place from the Equator, either towards the North, or South, Pole, can never exceed 90 degrees; and, that every line of Latitude, inasmuch as it remains always parallel to the Equator, is therefore called a Parallel:-thus we say the parallel of London, the parallel of Rhodes, &c. meaning to say, the line of latitude which runs through London, or Rhodes. Places situated on the Equator itself are said to have no latitude. 5. The Longitude of a place is its distance from a given spot, due East or West, and is measured either on the Equator, or on some circle parallel with it. The meridian of this spot is called the First Meridian, and was placed by the ancients, at the Fortunate Islands, because they were unacquainted with any land farther Westward; but modern nations generally adopt the capitals, or observatories of their own countries as first Meridians, thus, the English reckon their longitude from London, or the Royal Observatory at Greenwich, the French from Paris, the Spaniards from Madrid, and so on. The line, which marks the longitude of a place, is called its Meridian, from the Latin word meridies2, noon or mid-day, because, when the Sun passes this circle, it is noon in all the places situated under it; for, as this line of longitude compasses the whole earth from pole to pole, there must be several places under the same meridian. A place is in East Longitude from the First meridian when it is East of it, and in West Longitude, when it is West of it; for example, Rome is East, whilst Lisbon is West, of London. And, as the first meridian not only extends from pole to pole, but goes round the whole Earth, thus dividing it into two equal parts, called the Eastern and Western Hemispheres; and, as the whole circumference of the Equator (and of all the parallels which this first Meridian cuts in two) is 360 degrees, therefore, the half of this, that is 180 degrees, is the greatest longitude, which a place can properly have either East or West. Places situated under the first meridian are said to have no longitude. 6. The application of the terms Latitude and Longitude arose from the ancients being acquainted with a much greater extent of the Earth's surface East and West, 2 Inclinare meridiem Sentis? Hor. Carm. III. xxviii. 5. than they were North and South; and hence, they properly used the term longitude or length, to denote the greater dimension, and latitude or breadth, to denote the smaller. But our increased knowledge of the Earth has entirely done away with this distinction, excepting so far as the polar diameter being shorter than the equatorial, still renders the application of the terms just and proper. With respect to Longitude, it must be observed, that some still place the First Meridian at Ferro, the Westernmost of the Fortunate Islands, but this arrangement is so very inconvenient, that it is adopted only by a few. There are others also, who reckon the longitude entirely East or West (as it may be) round the globe, calling a place in 260 degrees East longitude, when it is actually in 100 degrees West longitude, and vice versâ; this may be easily remedied by subtracting the given longitude (say 260°) from the whole circumference (360°), and the remainder (100°) will be the longitude according to the ordinary method of reckoning. 7. From this it is evident, that a line running through any place, and passing over the poles, is the Meridian of that place; and that another line, running through it at right angles to this meridian, and parallel with the equator, is the Parallel of the same place: whence it follows, that there may be as many meridians and parallels as there are points on the earth's surface. It follows also, that as all meridian lines must pass over both poles of the Earth, therefore, there must be the same number of miles in every one of them; whilst, on the other hand, every parallel becomes smaller as it advances towards the poles, and, therefore, contains a less number of miles; for the pole itself is a mere point, whereas the equator is the greatest of all the circles of Latitude. This will be more apparent by referring to Plate I. in the Atlas, where the length of the line, which represents the Equator, is nearly nine inches long, whilst the parallel of 80° is not two inches. But it must be recollected, that, though there is not the same number of actual miles in every parallel of latitude, there are yet as many grees in it; for we have it laid down as a rule, that all circles (be they great or small) contain 360 degrees. Therefore, though the parallel of 80° is so much smaller than the Equator, it contains precisely as many degrees of longitude as the Equator does and places situated on this 80th parallel may be exactly in the same degree (say the 40th) of longitude, as places situated on the Equator; for this reason, because the meridian of 40° must, as it passes from the equator through the poles, intersect every parallel of latitude in the same respective point. It will be remembered, then, that all the circles of latitude and longitude contain the same number of degrees, and, that, these degrees, considered as parts of a circle, bear always the same proportion to each other; but, that whereas every degree of latitude contains 60 actual miles, the degrees of longitude contain a less number of miles in proportion as they advance towards the Poles. de 8. The number of miles and seconds contained in a degree of longitude, at every degree of latitude, will be found from the following table: |